Prostate cancer is a male-specific cancer, and according to the recent reports, the number of patients with prostate cancer has been considerably increased in Japan. Prostate cancer is known to relate closely to a male hormone (androgen).
Similarly, the number of patients with bladder cancer has been increased. As has been known, men develop bladder cancer more frequently than women do.
In one conventional treatment method for such urinary cancers, the organ of interest has been extirpated from the patients. For treating prostate cancer, an anti-androgen drug has been administered to the patients. However, the treatment method involving the extirpation of the organ considerably deteriorates the QOL of the patients. In the treatment method employing the anti-androgen drug, the cancer cells tend to acquire resistance to the drug in the course of treatment, and thus, the prognosis of the patients is severely degraded.
Also, the number of patients with kidney cancer, which is another urinary cancer, has recently been increased. Although radiation or anticancer drugs are employed for treating kidney cancer, a good outcome cannot be obtained. Meanwhile, in recent years, a considerably increased number of people suffer from breast or uterine cancer, in which estrogen—one female hormone—acts as an exacerbation factor. Many breast or uterine cancers become intractable as a result of acquisition of resistance to a therapeutic drug. Furthermore, lung, colorectal, liver and skin cancers are also difficult to treat, and involve the same problems as described above. The treatment of such cancers is of considerable clinical importance.
In order to overcome the above-described problems in such conventional treatment methods, there is a need to reveal the underlying mechanism of prostate, bladder, lung, colorectal, liver, uterine, breast, skin and kidney cancers and explore a new molecular target on the basis of that mechanism.
Meanwhile, in recent years, many attempts have been made to apply, to a cancer therapy, a technique of RNA interference (RNAi) which can suppress the expression of a target gene in a sequence-specific manner by introducing into cells a small-molecule RNA of about 18 to about 29 bases (short interfering RNA (siRNA)). Actually, many literatures report that the proliferation of cancer cells can be inhibited using siRNA targeting the gene involved in the cancer (see, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 2006-500916 and 2006-528618, and Ogushi T, Takahashi S, Takeuchi T, Urano T, Horie-Inoue K, Kumagai J, Kitamura T, Ouchi Y, Muramatsu M, Inoue S: Estrogen receptor-binding fragment-associated antigen 9 is a tumor-promoting and prognostic factor for renal cell carcinoma. Cancer Res. 65: 3700-3706, 2005.).
As has been reported by the present inventors (Ogushi T, Takahashi S, Takeuchi T, Urano T, Horie-Inoue K, Kumagai J, Kitamura T, Ouchi Y, Muramatsu M, Inoue S: Estrogen receptor-binding fragment-associated antigen 9 is a tumor-promoting and prognostic factor for renal cell carcinoma. Cancer Res. 65: 3700-3706, 2005), siRNA (siEBAG9C) targeting EBAG9 gene—a possible gene which allows cancer cells to avoid attacks by the immune system—can effectively suppress tumor formation of mouse kidney cancer Renca.
However, regarding a technique of RNAi, it is generally known that the expression suppressive effect on the target gene may greatly change depending on the base sequence of siRNA, and on the type of tissues or cells into which siRNA is introduced (see, for example, Kumiko Ui-Tei, Yuki Naito, Fumitaka Takahashi, Takeshi Haraguchi, Hiroko Ohki-Hamazaki, Aya Juni, Ryu Ueda, and Kaoru Saigo; Guidelines for the selection of highly effective siRNA sequences for mammalian and chick RNA interference Nucleic Acids Res. 2004; 32: 936-948.; Petr Pancoska, Zdenek Moravek, and Ute M. Moll; Efficient RNA interference depends on global context of the target sequence: quantitative analysis of silencing efficiency using Eulerian graph representation of siRNA. Nucleic Acids Res. 2004; 32: 1469-1479.; Olga Matveeva, Yury Nechipurenko, Leo Rossi, Barry Moore, Pal Saetrom, Aleksey Y. Ogurtsov, John F. Atkins, and Svetlana A. Shabalina; Comparison of approaches for rational siRNA design leading to a new efficient and transparent method. Nucleic Acids Res. 2007; 35: e63.; and Kathy Q. Luoa and Donald C. Chang; The gene-silencing efficiency of siRNA is strongly dependent on the local structure of mRNA at the targeted region. Biochem. Biophys. Res. Commun. 318 (2004) 303-310.).
For example, the present inventors studied on whether or not the aforementioned siEBAG9C exhibited a suppressive effect on not only the proliferation of kidney cancer cells but also the proliferation of prostate and bladder cancer cells. As a result, the present inventors have clearly found that, although the siEBAG9C exhibited a somewhat suppressive effect on prostate and bladder cancer cells, it could not exhibit a satisfactory suppressive effect (see Examples given below).
Also, it is difficult to select the target base sequence of siRNA so as to be completely different from all the gene sequences other than the target gene sequence. As a result, such a problem arises that gene expression is suppressed in a non-specific manner, which is called an “off-target effect.”
Thus, in order for the RNAi technique to be actually applied to therapy of prostate, bladder, lung, colorectal, liver, uterine, breast, skin and kidney cancers, there is a need to develop an excellent siRNA which exhibits a remarkable suppressive effect on prostate, bladder, lung, colorectal, liver, uterine, breast, skin and kidney cancers. Therefore, at present, further studies have been required on the selection of the target gene and the detail base sequence.